In general, repeaters are installed in areas in which signals transmitted from a main transmitter are weak in order to solve unstable reception and expand the transmission range of the signals.
When receiving a signal from the main transmitter, the repeater frequency down-converts the received signal to an intermediate frequency signal based on a local oscillating frequency and up-converts to the intermediate frequency signal based on the local oscillating frequency to an output frequency.
The repeaters use the local oscillating frequency when frequency converting. However, each local oscillating frequency of the repeaters includes a local oscillating frequency error that is different from an ideal value. In this case, when an output frequency of the repeater is different from its input frequency, the local oscillating frequency error is included in a transmitting signal. Since the local oscillating frequency errors have a different value by each repeater, if the transmitting signal includes the local oscillating frequency error, the output frequencies of the transmitting signals are different between the repeaters.
As a result, the errors between the output frequencies of the transmitting signals between the repeaters have a negative effect on reception performance of a receiving apparatus located in an area where areas of repeaters are overlapped
In order to reduce the errors between the output frequencies of the transmitting signals between the repeaters, the same local oscillating frequency should be used in the plurality of repeaters or the repeaters should cancel the local oscillating frequency errors themselves.
To provide the same local oscillating frequency to the plurality of repeaters, generally, a GPS signal processed through a PLL (phase-locked loop) is provided to each repeater as the local oscillating frequency. This allows the local oscillating frequency of each repeater to be the same and then it is possible to minimize the errors between the output frequencies of the transmitting signals.
However, on average, the output frequency of the repeater becomes stable while a momentary change in the output frequency, that is, a frequency jitter, is caused when the GPS signal is generated as the local oscillating frequency. Accordingly, the errors between the output frequencies of the repeaters may momentarily become large.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.